To provide users access to a mainframe computer, a host terminal application executing on a computer terminal with limited data processing capability was used to input commands and receive output data from a mainframe computer, replacing the use of punch cards. The computer terminal communicated with the mainframe over a serial data link and displayed information to the user as lines of fixed-width characters. Typically each line displayed 80 characters. Since the characters were fixed-width, characters could be formatted in columns and the formatting would be displayed the same on any computer terminal. As the use of personal computers became more prevalent, host terminal applications were executed on personal computers, replacing the computer terminal. A host terminal application executing on a personal computer enabled a user of the personal computer to communicate with a mainframe computer as if the user were using a computer terminal connected to the mainframe computer.
Today's business users have grown accustomed to the ease of use of modern Web-based applications. Hypertext Markup Language (HTML) conversion technology is used with legacy host terminal applications to provide a quick and easy way to replace traditional displays with a familiar point-and-click interface. HTML conversion technology enables the proven, reliable host terminal applications, which are comparatively more difficult to learn and use, to be modernized with more familiar rich client applications and web-based applications having a graphical user interface.
Mobile data processing systems such as personal digital assistants (PDAs) are becoming more widely-used. PDAs are small enough to fit in the palm of a user's hand. As a result, display sizes are much smaller than a traditional personal computer. When a PDA having a smaller screen is used with legacy host terminal applications and HTML conversion technology, the smaller screen size of the PDA causes usability issues. Host terminal applications were designed for use with computer terminals, which are capable of displaying 80 characters or more in a line. PDAs typically cannot display 80 characters per line in a readable manner. One possible solution is to use a horizontal scroll bar. However, many mobile users prefer scrolling only in the vertical direction and not in the horizontal direction. Another solution is to reduce the size of the application window (effectively “zooming out”). But the small nature of PDA displays limits the extent to which an application window can be reduced while remaining readable. Mobile web browsers (e.g., Internet Explorer Mobile) have their own screen compression options for displaying HTML code. But the screen compression options are designed for displaying web pages, and are not well suited for displaying host terminal applications.